Substrate-type optical waveguides, in which function elements such as modulation elements and switch elements are provided, are widely used. Typical examples of the substrate-type optical waveguides encompass silicon waveguides (see Non-Patent Literature 1). Such a function element is ordinarily designed to effectively fulfill its function in a case where transverse electric (TE) light is inputted into the function element. This is because (i) TE light allows the power of light, which is to be confined in a core of a substrate-type optical waveguide, to be larger in comparison with the case of transverse magnetic (TM) light and (ii) TE light reacts more acutely to a change in refractive index of a core in comparison with TM light.